1) Field of the Invention
The present invention relates to an optical switch apparatus and optical switching system suitable for constructing an optical communication system capable of handling a large volume of information in the form of optical signal without temporarily carrying out a conversion into an electric signal, and more particularly to an optical switch apparatus and optical switching system suitable for use in a network designed to conduct optical burst signal processing.
2) Description of the Related Art
In the case of a photonic network in a metroaccess area, a network configuration is frequently changed through switching/route switching on lines or signals for ADM (Add Drop Multiplexing) or the like. In the present networks, many repeating stages have employed a configuration to carry out signal switching by conducting a conversion into an optical signal after an optical signal is once converted into an electric signal.
However, in the future, from the viewpoint of improvement of performance of a network, it is expectable to achieve the replacement with a dynamic OADM (Optical Add Drop Multiplexing) device made to demultiplex only desired wavelengths as an optical signal is kept intact, an optical cross connect node made to conduct the switching of input/output routes in units of wavelengths in the form of an optical signal or other devices in light of speeding-up of switching processing.
In addition, in the next generation, for the enhancement of line using efficiency, it is considered that there is a need to provide a function whereby an optical signal is divided into frames each having a given length and switching/route switching processing (in this specification, a general term of these processing will be described as optical burst signal processing) is conducted in units of the divided frames as an optical signal is kept intact.
In a transmission apparatus made to handle such optical burst signal processing, for carrying out the switching or route switching in units of frames as mentioned above, it is expected to conduct the switching processing in a time dimension smaller than at least milli-second dimensions.
As well-known techniques related to the present invention, there are the following patent documents 1 to 6.
(Patent Document 1) Japanese Patent Laid-Open No. 2002-318398
(Patent Document 2) Japanese Patent Laid-Open No. 2003-185984
(Patent Document 3) Japanese Patent Laid-Open No. 2000-114629
(Patent Document 4) Japanese Patent Laid-Open No. 2000-269892
(Patent Document 5) Japanese Patent Laid-Open No. HEI 7-212315
(Patent Document 6) Japanese Patent Laid-Open No. HEI 10-228007
Assuming that, as described above, the switching processing is conducted in units of frames in a time dimension smaller than milli-second dimensions, there is a need to continuously conduct the route switching on frame signal lights inputted from various routes. At this time, due to differences in input power, differences in loss among optical switch ports and other factors, differences in output power value of the frame signal light occurs among the output ports, which can create troubles in a case in which error-free reception is made in an optical receiver.
The techniques described in the above-mentioned patent documents 1 to 6 do not disclose a configuration designed to eliminate the differences in frame signal light output power value among output ports in the case of carrying out the switching processing in units of frames in a time dimension smaller than milli-second dimensions.
Although the foregoing patent documents 3 to 6 disclose a variable optical attenuator which variably controls an attenuation quality of output light in a feedback fashion, in the case of such feedback control, difficulty is encountered in executing control so as to make the output power value constant on frame signal light for conducting the switching processing in a time dimension smaller than milli-second dimensions. This is because the signal light passes through it at the time that the feedback control takes place.
In a switch node in which the route switching is conducted through the use of such optical burst signal processing, if the optical route switching can be conducted without carrying out the optical-electrical-optical conversion and the output power can be made constant, it is possible to facilitate a design of network apparatus (in particular, downstream-side apparatus) other than this switch node. In addition, in this switch node, if the wavelength switching can be conducted for each frame signal light, it is possible to construct a more-flexible photonic network.